1. Field of Invention
This invention relates to defending aircraft against missile attack.
2. Introduction
Heat-seeking MANPAD (Man Portable Air Defense) systems such as the FIM-92 Stinger missile present a critical and pressing terrorist threat to commercial air transport aircraft. The most vulnerable phases of flight are during landing approach and immediately after takeoff. Also many landing approach profiles require prolonged flight at low altitudes over populated areas. Nevertheless, although the stakes are high, the probability that any particular transport would ever be attacked is very low. For society, this situation produces a cost-effectiveness conundrum. A desirable missile defense system for transports must operate continuously, effectively, reliably, and economically.
Various systems have been proposed to defeat infrared (IR) missile threats. Pyrotechnic flares are used traditionally for this purpose, but have short effective time durations. Routinely dispensing flares to draw possible MANPAD missiles away from a transport is clearly unacceptable. Dispensing flares or recoverable decoys when an attack is detected requires a sophisticated and costly missile attack sensing system. Recurring false alarms would likely cause unacceptable hazards from flares to people and property. Tethered decoys have also been proposed. Non-predeployed recoverable decoys must be deployed quickly after receiving a warning, which places stringent requirements on the tether line and requires a complex release and recovery system. Decoys must also radiate considerable IR power, which limits operating duration or requires significant power-carrying capacity by the tether. Fueled decoys must be refueled and battery-operated decoys need to be recharged or replaced, requiring costly and time-consuming ground operations. Another issue is handling potentially hazardous materials at passenger terminals.
To be effective, a passive decoy must radiate IR energy at levels comparable to or exceeding that of an airliner. The hot parts (mainly the turbine plates) of transport aircraft engines present areas of about 0.5 m2 at temperatures ranging around 750 K radiating at about 1500 W/sr, primarily in the rearward direction. (See Volume 7. Countermeasure Systems, Pollock, David H., ed., 1993, pp. 242–245; & The Infrared and Electro-Optical Systems Handbook, Infrared Research Analysis Center, Environmental Research Institute of Michigan, Ann Arbor, Mich., and SPIE Optical Engineering Press, Bellingham, Wash.)
Active jamming systems, including Directed InfraRed Counter Measures (DIRCM), have also been strongly advocated. A typical proposed DIRCM system comprises three principal components: (1) a missile attack warning system; (2) data processing system; and, (3) a directed high-power laser in a gimbaled turret. At an estimated cost of $1–2M or greater per aircraft for such systems, outfitting the 7000-aircraft US commercial transport fleet is clearly an extremely expensive proposition.
A cost-effective, long-term realistic solution addressing terrorist threats inherent in the existence of simple heat-seeking man portable missile systems, whether defensive or offensive, is urgently needed.
My invention system of deploying and retrieving a self energized, radiating decoy from a host commercial aircraft during vulnerable stages of a flight can provide significantly lower initial and lifetime costs as well as effective protection against terrorist MANPAD attacks. The mere presence of such a system would decrease the likelihood of such attacks because the probability of a successful kill would be significantly reduced without affecting the probability of detecting contemplated attacks planned by terrorists. Most importantly, existing commercial air transport fleets can be easily and relatively inexpensively, retrofitted with the invented system enabling defense and protection of transported civilians at an early date.
Description of Prior Art
Traditional systems for heat-seeking missile defense commonly dispense flares or similar munitions as decoys. For example, U.S. Pat. No. 3,150,848 to Lager discloses energy-radiating masses comprised of metered pyrophoric and oxidizer substances ejected in pulses to decoy heat-seeking missiles. U.S. Pat. No. 4,498,392 to Billard et al. teaches a chain of sequentially ejected pyrotechnic decoys. U.S. Pat. No. 5,074,216 to Dunne et al. discloses a stabilized infrared decoy flare designed to reduce tumbling and cooling after ejection into the airstream. U.S. Pat. No. 5,565,645 to Tappan et al discloses a high-intensity infrared decoy flare that employs unstable combustion during the first 0.2–0.5 second after ejection and ignition. Peak intensity of IR radiation emitted initially by the flare is said to be 826 watts/steradian. During later stable combustion the IR radiation is said to be 450 watts/steradian. These radiation levels are similar to those of jet transport aircraft engines.
U.S. Pat. No. 6,663,049 to Jakubowski et al and U.S. Pat. No. 6,352,031 to Barbaccia describe radiative countermeasures using on-board fuel supplies.
Numerous disclosures teach tethered decoys and means for deploying and recovering tethered decoys. Examples include U.S. Pat. No. 5,136,295 to Bull et al, U.S. Pat. No. 5,570,854 to Brun, U.S. Pat. No. 5,683,555 to Carlson et al, and Patent Application Publication U.S. 2003/0071164 by Carlson et al. U.S. Pat. No. 6,662,700 to O'Neill describes a string of burning flares stored in a dispenser towed behind an aircraft along with a sensor to activate them when a threat is detected.
U.S. Pat. No. 5,497,156 to Bushman discloses a towed target that collects and selectively reflects IR energy from the exhaust plume of a jet engine immediately ahead of the target in order to attract missiles. This is said to produce a greater heat signal that from the engine itself.
U.S. Pat. No. 6,267,039 to Czarnecki discloses an IR lamp mounted on a sacrificial portion of the aircraft structure itself. A missile attracted to the lamp will damage or destroy the sacrificial structure but hopefully not bring down the airplane. The lamp is powered directly by the aircraft electrical system. Czarnecki does not mention deploying the lamp away from the aircraft nor self-powering the IR lamp. Patent Application Publication U.S. 2003/0116050 by Brum et al discloses an electrically heated radiation augmenter to attract heat-seeking missiles to a towed body. The augmenter is said to operate at 1400 F (1050 K) emit 40 watts/steradian in the 3–5 micron band. Assuming a grey-body Lambertian surface and emissivity=1, the surface area of the Brum emitter is only about 50 cm2. Therefore, both the radiating area and radiant intensity of the Brum emitter are very small (1%) compared to those of a transport jet engine. The power source for the heater is not described but is said to be either internal or provided externally by means of the tow line. Brum et al do not disclose use of an internal or external turbine or alternator.
U.S. Pat. No. 5,333,814 to Wallis teaches a maneuverable towed body for intercepting missiles. The Wallis system requires active missile detection and tracking means to maneuver the decoy into the path of an attacking missile, but the actual means are not discussed. The maneuverable body contains small IR emitters for attracting missiles and employs a propeller beyond the tail as a conventional external ram air turbine (RAT) to power the body. Wallis provides no details regarding the generator and does not teach an IR decoy with an internal switched or variable reluctance integrated turbine-alternator, a system for deploying and recovering the decoy, or storing the decoy in a low-drag configuration.
Switched or variable reluctance generators are especially useful in aircraft applications due to their relative lightness. These are often used as emergency power sources. U.S. Pat. No. 5,899,411 to Latos et al describes an emergency power system using a wind-driven turbine. U.S. Pat. No. 6,467,725 Coles at el discloses a switched reluctance generator geared to a “windmilling” turbine engine spool to produce emergency power. U.S. Pat. No. 5,327,069 to Radun et al, U.S. Pat. No. 5,606,247 to Sutrina, and U.S. Pat. No. 6,724,114 to Horst disclose typical embodiments of switched reluctance generators and motors that use multi-pole stators and cogged-teeth rotors. None of these disclosed or suggested turbine-alternator rotor/stator vanes providing variable reluctance electromagnetic circuits for powering radiative arrays.
U.S. Pat. No. 5,544,484 to Voss et al discloses a combined turbine-alternator that includes stator blades with magnetic cores. Induction coils wound on or around the stator blades generate electrical power. Moving permanent magnets attached to a magnetic rotor disk complete the magnetic circuits of the generator/alternator. Voss et al do not discuss or disclose magnetic rotor blades comprising part of a magnetic circuit carrying flux from a stationary permanent magnet or from an electromagnet (Voss et al actually teach plastic rotor blades). Voss et al primarily teaches regulation of alternator output mechanically by controlling the airflow through the turbine. Voss et al also discloses compensating for variable turbine-alternator outputs by electronically adjusting a conventional alternator co-attached to the electrical output of the turbine-alternator. However, Voss et al does not disclose or discuss directly regulating the combined turbine-alternator by electrical or electronic means.
U.S. Pat. Nos. 6,683,555, & 6,779,796 to M. A. Carlson et al each describe and teach variations of decoy deployment and retrieval systems from flying aircraft that contemplate deployment, retrieval and redeployment of a tethered decoy, over and over again responsive to detected threats in the course of military missions in appreciation of the fact of range and maneuverability penalties inherent in a tethered decoy, and the large cost penalties inherent in cutting loose (sacrificing) a deployed tethered decoy after a detected threat abates or is abated.